Is It The End For My Inboard???

dauntlessman

dauntlessman

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Falmouth, Cornwall
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Hello people,

Recently my engine has been riddled with problems. Last time it was fuel (starvation) problems, which you guys kindly helped me out with and I have since replaced the tank.

The engine is a (very old) Renault diesel, single cylinder, 8 HP unit.

Anyway I took her out for her test up the river Fal and what had started out as good - soon turned bad. Though I am now convinced that the fuel starvation problems have been remedied, what looks to be a much more serious issue has taken hold.

With the engine running at idle (out of gear), it sounds relatively smooth with no major smoke or unusual noises and cooling water running nicely through the stern exhaust. If I put it into gear it chugs along reasonably well but only at very low throttle.

As soon as I give it any kind of throttle (to get her moving quicker than approx 1.5 knots), I have seen pretty substantial amounts of black smoke pouring out of the exhaust! Presumably this indicates a substantial amount of oil being burnt. Note that this only at higher RPM.

Unless you guys can make my day and come up with a reasonable explanation for this, I reckon it’s knackered and I’m not sure if it’s worth getting fixed. Spending any more than a couple of hundred just seems a bit of a waste given it’s age etc.

We continued our little jaunt using my Honda 2 HP outboard, which actually pushed her along quite well given that she, weighs a couple of tonnes. I’m not to sure about this as a permanent measure and it’s pretty clear that this is not a very economical way of covering larger distances.

Any advice on either the options for the inboard or the effectiveness of my little 2 HP would be gratefully received. I’ll be floating about for Falmouth week anyway so I guess that will put the outboard through its paces!
 
I would imagine it's unburnt fuel if the smoke is black, and that it's your injector that is shot. It may be possible to have it rebuilt or get an exchange one.
 
If its black smoke, its unburnt fuel pouring out of the exhaust.
It sounds like its overfuelling on higher throttle openings, so maybe injectors wedged open with a lump of crud, or damaged. Is the air inlet blocked in any way?

If its blue, its oil. If you get a large puff of blue smoke when you come off idle, and then see no more, then its probably valve guides, if its a steady stream of blue smoke, its probably piston rings.

From your description, its not serious, fuel or air related.
 
Oh, thats quite interesting given I have just replaced the tank.

Presumably, as the engine was being starved of fuel before, this problem didn't occur. Now it's got all the fuel it can handle, it's trying to burn too much?

If this is the case, is it a DIY job or something for a pro? I am still pretty useless but learning very quickly...
 
To some degree all diesels produce black smoke when opened up suddenly. Fuel injection on a diesel is mechanical, so opening the throttle gives the engine more fuel than it can suck air in to burn. There three other problems that could also give rise to this.

1/ Injectors that instead of atomising the fuel are simply letting it into the engine in a dribble. Some fuel will then not burn. Solution - remove the injectors, take them to a diesel injector shop (yellow pages) and have them cleaned and re-set.

2/ High load at low revs from, for example, a fouled prop. The engine gets fuel to rev faster but cant actually speed up. So too much fuel for the air again. Solution : find the load and remove it.

3/ Blocked air filter not letting enough air in to burn the fuel.

The classic mistake we all make is to ignore the simple cheap problems and jump to the conclusion that its something expensive and terminal. If your engine starts well, pumps out cooling water OK, doesnt burn lube oil, then its likely a minor problem. Certainly even the marina diesel mechanic is worth a go before thinking of new engines.
 
My vote would be for a fouled propeller. This would overload the engine and it would blow black smoke.

I recently picked a plastic sand sag, and the engine (ford petrol) would run fine at or just about tickover, but would go no faster even with the throttle wide open. There wasnt even any undue vibration from the prop, but i knew what had happened.

Simple things first, complicated things (like injectors) later.

Id also check for over tight stern glad, gearbox ok etc first too. Its not a powerful engine, so it wont take much to stop it turning.
 
check the air filter and make sure you don't have an exaust leak near the intake as this crates a visious circle of blockage, black smoke, more blockage etc etc.

Yoda
 
I think Spyro has the answer, check the exhaust, if it will rev to its normal speed out of gear but no power and smoke in gear it could be air starvation...... if the exhaust is restricted not enough air will be entering the cylinder.
On my engine it coked up to about a 1/4" hole instead of 40mm (sorry about the mixed dimensions!)
 
Your fears are ill placed - as others point out, it is simply overfueling. Just about all the likely causes have been suggested, but I'd suggest the sequence to check is start with simple things, and work up. Simplist is lack of air (clean air filter) followed by fouled prop (clean), dirty hull (clean and antifoul), restricted exhaust (remove, and decoke or replace with new) and with last being the injector needs a rebuild (will cost some money). Do the simple ones yourself, and then decide at which point you need to get a local diesel mechanic involved. It could be that the engine is simply clogged up with carbon and soot - has it had a decent run, and if not, once air/prop/exhaust done, go for a decent run with the engine at full throttle for 15 minutes - it'll belch like crazy to start with, but may well clear and improve. BTW how long since the engine had a decent service? If a long while then there's a good start, as small diesels are great but they do like to be treated regularly.
 
Black smoke is rarely a serious problem - and certainly not symptomatic of a dead engine.

Does it rev out to full speed out of gear without making black smoke? If so possibly the prop is fouled, or the injector needs re-setting. If not, the exhaust may be blocked, the injector may need re-setting, the air intake is blocked, or the injection pump has a fault.

Check also that all the fuel lines are completely fuel tight - use a coloured paper tissue, clean the joints thoroughly, run for a few minutes, then wipe with the tissue. Any trace of fuel will darken the paper, and will be upsettng the engine
 
Black smoke is usually oxygen starvation, it is pure carbon being emitted rather than CO2 - the cause being not enough O2.

Most common cause for this to develop in service would be blocked air filter - try a test with it removed.

Also could be blocked exhaust or elbow - trickier to diagnose without removing elbow and hard to find out if exhaust has de-laminated on the inside somewhere to cause a restriction.

Other causes could be not enough air supply to engine space due to new soundproofing for instance.

Secondary reason could be overloading. This happens when you open her up and more diesel is introduced, but the engine can't rev up enough to supply the necessary air to burn it. If you haven't fitted too small an engine or too large a prop., this prognosis would relate to a dirty hull, fouled propellor or partially seized gearbox or shaft.

What you are not descibing is an engine wear problem due to burning engine oil which is visibly blue, or an injector with a poor spray pattern (which will have lighter blue/grey colour and will stink rancid of unburned but vapourised diesel).

As a slight aside, if the alternator is large in relation to the engine, and the battery(s) are low in charge, the amount of load placed on the engine by the alternator can be sufficient to hold back the engine when in gear, but not when in neutral.

My alternator produces maximum charge at 1500 engine rpm, and with flat batteries absorbs about 1hp. At 1500 rpm the engine is probably producing 3, 4 maybe 5hp so you may understand the issue. Are your batteries well charged?
 
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